Plastic containers have now come into wide-spread usage as vessels for liquids, such as milk and the like, often substantially completely replacing glass bottles and the like. Certain types of plastic containers have been found to be more suitable than other types of plastic containers for use in applications wherein a relatively high degree of mechanical and automated processing is involved, such as automatic filling procedures.
In this connection, plastic containers of a one-piece blow-molded construction having four generally flattened sidewalls interconnected by curved corner portions have come into wide public use. The handle is integral with the container and constructed as to not extend beyond the side elevational profile of the container in any given direction so that regardless of how the container is fed into a holder, automatic filling device, or the like, the container handle does not interfere with container utilization. Such a container has associated with it a high degree of standardization as respects size, mouth location, internal volume, etc.
As the cost of the thermoplastic resins increases with the rising costs of petroleum (many thermoplastic resins being comprised of one or more components derived from petroleum directly or indirectly), an increasingly important need arises to cut the cost of the plastic containers. One way to reduce cost is to reduce the quantity of plastic required in a given plastic container without adversely affecting the strength and rigidity characteristics thereof. Since a great deal of capital investment has been made in, for example, automated equipment adapted to use plastic containers having generally flattened sidewalls, it would be highly desirable to reduce the amount of plastic required in such a type of container without adversely interfering with the strength and rigidity requirements thereof.
Production of lightweight bottles has been achieved generally only by reducing surface wall thicknesses. However, the thinner the walls the more susceptible they become to failure from normal hydrostatic forces exerted upon a filled container. The lightweight containers presently available have gone as far as they can in reducing bottle weights in this manner. Below the present levels of minimum weight, failures, usually in the form of surface creases or kinks, would regularly develop as the result of hydrostatic forces in filled bottles. These failures do not always lead to rupture or spillage; however, any kinking or other type of distortion in a plastic container construction is undesirable. For one reason, it tends to represent a weakness or potential for breakage in the mind of consumers, thereby negatively affecting the salability of the container and its product.